Long-term effects of consumption of low-copper diets with or without supplemental molybdenum on copper status, performance, and carcass characteristics of cattle.

We used 42 Angus bull calves (7 mo of age) to determine long-term effects of low Cu diets with or without supplemental Mo on performance, carcass characteristics, and Cu status. Twenty-two bulls were injected with 90 mg of Cu 28 d before weaning. After weaning, injected steers were fed a diet supplemented with 7.5 mg of Cu/kg of DM; control steers received no supplemental Cu. At the end of the 40-d receiving phase, supplemental Cu was reduced to 5 mg/kg of DM. One half of the steers in each group were fed 5 mg of supplemental Mo/kg of DM following the receiving phase. The growing phase lasted 196 d. Steers were then switched to a high concentrate finishing diet for 49 d. Copper injection increased (P < .01) plasma Cu concentrations at weaning, and Cu-supplemented steers had greater (P < .05) plasma Cu, ceruloplasmin, superoxide dismutase activity (SOD), and liver Cu at the beginning of the growing phase. Supplemental Mo depressed plasma Cu, ceruloplasmin, and SOD during the growing and finishing phases in non-Cu-supplemented but not in Cu-supplemented steers. Copper supplementation increased DMI during the receiving (P < .05) and growing (P < .08) phases and increased (P < .08) ADG and gain:feed ratios during the finishing phase. Steers fed supplemental Cu produced carcasses with less (P < .06) backfat and slightly larger (P < .09) rib eye areas. The results of this experiment suggest that dietary Cu concentrations may alter cattle performance and carcass characteristics.